The feeling is growing in the international commentariat that the Islamic State may win: That the group will continue to gain territory in Syria and Iraq and will consolidate a permanent government, a state ensconced in the Islamic caliphate its leadership has proclaimed. I ended a recent article on a note of bravado, writing that in spite of its successes on the battlefield and elsewhere, it remains all but certain that Islamic State will ultimately be ground up and destroyed. Today I am less certain, and I have started to imagine what would happen if ISIS actually prevails.

I am reconsidering for a simple reason: U.S. Secretary of Defense Ashton Carter's contention that the Iraqi government's military forces show "no will to fight." In a June 1 editorial titled "Who's willing to fight for Iraq?" the New York Times suggested that if Baghdad's military is unwilling or unable to defeat ISIS - if it is outgunned, out-organized, out-strategized and, one must add, terrorized by ISIS savagery - outsiders should stay out. No boots on the ground, no escalation of air strikes; let us limit wasted resources.

What would result from an ISIS victory? First, an official Sunni Muslim state would be consolidated, straddling the post-World War I Sykes-Picot Syria-Iraq border whose very existence exemplifies for the Islamic State how Middle Eastern geopolitics was unilaterally rearranged by European powers. The battlefield would decide exactly how much of Syria and how much of Iraq would fall under the state's control. In Iraq, the Islamic State would incorporate all Arab Sunni areas, beginning with Anbar, the largest Iraqi province. Kurdistan would be left alone, at least for the time being. The Peshmerga army, beefed up by the United States and highly motivated because the Kurdish fighters are defending their own territory, would be a fierce opponent for ISIS, whose leaders are rational strategists.

Iraq south of Baghdad - that is, the country's Shiite-dominated area - would also be left unchallenged for the time being. ISIS is a Sunni entity and aspires to destroy Shiism worldwide, but, like the Peshmerga, Iraq's Shiite militias are battle-ready, and they hate Islamic State viscerally. Moreover, there is the Iran factor. Tehran is backing Iraqi Shiites - providing weapons and personnel - and ISIS will not want to challenge Iran, so will avoid attacking Iraqi Shiite territory. Whether to target Baghdad itself will be a strategic decision for ISIS. (Council on Foreign Relations President Richard Haass considers Baghdad already part of a Greater Iran.) Turkey, for its part, has already accepted Islamic State control over substantial territory along the Turkish-Syrian border. Ankara did not engage ISIS when the group attacked the Syrian Kurdish border town of Kobani, and Ankara has little reason to fight to save Syrian territory now, especially since it wants the Assad regime demolished. A victorious ISIS furthermore would have defeated and/or incorporated the various anti-Assad rebel groups, including the so-called moderates as well as al Qaeda-linked formations.

Nevertheless, as with Turkey, the Islamic State logically at some future point would attack Iran. The Islamic State's goal is to reign over the entire Muslim world of believers, the umma, in a Sunni caliphate centered on Sunni beliefs and Sunni interpretations of the Koran. Iranian society is Persian and overwhelmingly Shiite; Turkey is Sunni, but comprises mainly Turkic peoples, along with a Kurdish minority accounting for 15 percent of the population. One must also eventually consider nuclear proliferation issues, and question the Islamic State's relation to the nuclearization of the Middle East. Would an ambitious Islamic State not require nuclear weapons to face Iran (and Saudi Arabia)? What would the United States and Israel do if it began to pursue them?

A Regional Breakdown

If ISIS wins its wars in Iraq and Syria, Iraq will have effectively broken down into its three historical ethnic-religious regions: a majority-Shiite south, a Sunni-Kurdish north, and a Sunni-Arab west. An international conference to legally redraw boundaries would be unnecessary and in any case anathema, to the Islamic State and outside powers alike.

For Washington, Tehran, Ankara, and the Europeans, considering whether to intervene decisively in Syria and Iraq means thinking not only about who is willing to fight, but also about who is willing to pay to rebuild those societies if ISIS is crushed. The re-establishment of institutions and infrastructure is a huge enough task, and it is but one aspect. The human dimensions are much greater: It is estimated that half of Syria's population is displaced, most of them living somewhere on the national territory, but with millions of others living in other countries - for example Turkey and Jordan, which also house large Palestinian refugee populations. Adequate food, housing, and medical and energy services are necessary - not to mention getting hundreds of thousands of children back into schools that would need to be rebuilt. (Several months ago it was estimated that the Islamic State had about 600,000 children in its grasp, educating them in a Sharia-based curriculum.) How many exiled Syrians and Iraqis would return home from abroad is an open question.

Outside governments and international organizations might take on this burden for humanitarian and geopolitical reasons. But rebuilding, indeed recreating nations in Syria and Iraq would be a monumental project at a monumental cost that would require a commitment of many years, if not decades, and these countries have their own priorities as well.

Looking at things as they really are, it is obvious that the only government (or other organized force) willing, indeed eager, to take on this job is the Islamic State. That's the whole point for them: to assume the burdens of victory, which would, after an orgy of violence, prove their integrity of purpose. Providing food, health care, and housing is defined as such in their "mission statements," along with committing any savagery necessary to (in U.S. military terminology) "clean and hold."

Shared calculations

These calculations would explain the evident but tacit foreign policy shared by Washington, Tehran, and Ankara: Stay out and keep clear. Provide money and face-saving air and ground engagement, but let the war play out among the locals and plan for a future Middle East encompassing a powerful, dangerous, and unpredictable state hostile to everyone else. This includes extreme wariness about negotiating with it, which will be an issue at some point.

If this came to pass, displaced Syrians and Iraqis throughout those countries and the region would have to decide whether to continue their precarious lives among strangers or return home to life in a Sharia society run by Islamic State rules. Some might look to the city of Mosul, where ISIS for almost a year has run the municipality without collapse or great violence, presenting it as a prefiguration of caliphate society. ISIS in power provides jobs and pays salaries on time, whether to local officials or its fighters on the battlefield. Outside the region, everyone - and especially Americans for whom everything about Islam is unknown - should be aware that even for people who hate Islamists, ISIS rule offers a kind of stability. Comparable cases abound both in history and in the contemporary world.